Coated expandable polystyrene



United States Patent Office Patented Aug. 19, 1969 3,462,293 COATEDEXPANDABLE POLYSTYRENE William H. Voris, Mars, Pa., assignor to KoppersCompany, Inc., a corporation of Delaware No Drawing. Filed Nov. 7, 1966,Ser. No. 592,271 Int. Cl. B44d 1/48; B44c 1/06; C08d 13/24 U.S. Cl.117100 4 Claims ABSTRACT OF THE DISCLOSURE Expandable polystyrene beadsare uniformly coated with polymeric material to enhance the propertiesof the beads and articles made therefrom by a process comprisingsuspending the expandable beads in a stream of air at l-130 F. andcontacting the beads with an aqueous latex which dries in the heated airstream to form a uniform particulate or film coating.

Expandable polystyrene beads are a well known commercial item. Suchexpandable beads are useful in the molding of numerous low densityplastic articles. There still remains, however, some problems associatedwith the use of such expandable beads. For example, the expandable beadsemploying a volatile expanding agent tend to lose the volatiles onstorage. In addition to volatile loss, beads which are colored withvarious dyes also have the disadvantage of losing some of their coloringthrough leaching. Other problems associated with such expandable beadsare their tendency to lump during preexpansion and also the low abrasionresistance of articles formed from such expandable polystyrene beads.

Heretofore, processes for coating expandable polystyrene beads withresinous materials have resulted in a product which retains tackinessand must be cured before further processing, or in beads which arepreformed into a desired shape before further molding to the finalarticle.

I have discovered that expandable polystyrene beads can be uniformlycoated with polymeric materials by a novel process which results inbetter volatile retention of the unexpanded beads and also aids in theprevention of lumping during pro-expansion of such expandable beadsbefore molding. My process results in beads which have better dyeretention than uncoated beads and upon molding provide articles whichare abrasion resistant.

In accordance with the present invention, expendable polystyrene beadsare uniformly coated with polymeric materials by suspending the beads ina heated air stream and contacting the beads with an aqueous latex whichdries in the heated air to form a uniform particulate or film coating onthe beads. The beads so processed are discrete particles suitable forimmediate feeding into a mold for expansion to desirable foamedproducts.

The temperature of the air employed in the suspension of expandablepolystyrene beads must be such that there is little loss of volatilesfrom the beads, that is to say, little loss of blowing agentincorporated in the expandable beads, during the coating step.Temperatures in the order of 100 to 130 F. are used in the presentprocess, such temperatures causing little or no loss of volatiles fromthe expandable beads which are being coated, but still being atemperature at which the latex which is being used as a coating for thebead will dry on the beads.

The polymeric material employed as a coating for the expandablepolystyrene beads must be that which will form a coating on the beads atthe conditions employed during the coating process, which coating willnot be tacky at room temperature. If the coated beads are themselvestacky at room temperature, the beads will lose their ability to be fedas discrete particles into a mold in the formation of the expandableproducts. The coated beads may feel somewhat tacky to touch, owing tothe external heat which is provided by the human body temperature whilethe beads are held in the hand, although the beads may still be suitablefor feeding into a mold whereby the coated expandable beads are incontact only With each other.

Especially uniform and well coated expandable polystyrene beads areprovided which have imparted thereto various desirable improvements,both in the processing and manufacturing of useful foamed products andin the properties of the products as their unexpanded, expanded, andmolded or extruded foamed forms. Major process benefits derivable fromsuch coating of expandable polystyrene beads are the prevention of drysticking of expanded beads, prevention of lumping on pre-expansion, andan improvement in the storage life of both unexpanded and expandedbeads. The coated beads exhibit increased abrasion resistance overnormal expandable polystyrene beads, by the formation of a uniformcoating of polymeric material around the beads, whereby the beads uponexpansion form a molded object having a tough outer skin.

The coated expandable polystyrene beads prepared by the presentinvention have excellent anti-lumping properties. As is known in theart, expandable polystyrene heads have a tendency to stick together andform lumps during the pre-expansion process which renders the particlesunsuitable for molding. Heretofore, lubricants have been added to thesurface of the particles to alleviate this problem, but the amount oflubricant had to be carefully controlled. Such lubricants can alsointerfere with fusion of the beads on molding, and can reduce the shelflife of the particle due to a rapid loss of blowing agent, in additionto interfering with the free-flowing properties of beads because oftheir oily nature.

The latex used to coat the expandable polystyrene beads is preferablycomprised of a polymeric material produced from an ethylenicallyunsaturated monomer, such as ethylene, propylene, butylene, or styrene.The polymeric material may be a homopolymer of the above monomers or acopolymer. Also useful are acrylate polymers and acrylate copolymers ofethylenically unsaturated monomers. Especially useful polymericmaterials are polyethylene, polyvinyl chloride copolymers,polyethylacrylates and styreneacrylate copolymers.

The expandable polystyrene beads to be coated are commercially availableunder various trade names. The beads may be prepared, for example,according to DAlelio Patent No. 2,983,692. Such beads contain volatileorganic blowing agents such as pentane, hexane, cyclohexane, heptane,isopentane, and halogenated derivatives thereof, which agents boil belowthe softening point of the styrene polymer. Expandable polystyrene beadscontaining minor amounts of other polymeric materials such asstyrene-alpha-methylstyrene copolymers are also useable in theinvention.

The amount of polymeric material which is deposited on the expandablestyrene polymer beads should be between 0.5 and 15% by weight. Lesseramounts of coating does not result in sul'ficient improvement of theproperties of the resulting beads. Greater amounts are unnecessary asmicroscopic examination of the product of the invention shows thecoating to be deposited in a uniform manner over the surface of thebeads, so that minimum 4 Example 1V Tests were made to determine theeffect of the coating on the volatile retention of the expandablepolystyrene beads. Samples of the various compositions of Examples Tamounts of polymeric material provide the improved 5 i i i i g z i i ggi g g prOFeSs Y properties to the expandable styrene polymeric beads. Mycontginers 0110 i the f S f invention is further illustrated by thefollowing examples: g a p c655 W1 6 O lowing results: Example I 10 V 1t'l 1 t A quant1ty of Dyl1te F-40 expandable polystyrene a ft c yfilfifli beads were screened through a 16-mesh U.S. standard g fi ggscreen and held on a 25-mesh screen to obtain a mass of Compositionpercent percent storage beads of substantially uniform size. Theseexpandable Amontml) M 618 413 polystyrene beads are spherical and have aglassy smooth B 6.7 6.03 sag surface. The beads contained as expandingagent pentane g: 2:; 2 g i in the amount of 6.7% by weight of the bead.The mass E 6.7 5.95 GM of beads was acidified, washed and dried. Themass of beads had the following bead size distribution: All of thecoated beads WhlCh lost very little volatiles dur- 20 ing the coatingprocess, showed better volatile retention Pelcent g g than the controlsample, an important factor in the stor- 20 age of expandable beads. I:30.6 Example v 2 Th abrasion resistance of the compositions of E 1 65 Iand II were determined on the molded discs, by Aliquots of these beadswere employed in the process of determining the weight loss and wearindex, after 500 the invention and coated with the various laticesdescribed cycles With a Taber Model 503 Abrasion Tester. The rein theexamples below. One aliquot was set aside as a consults of the abrasiontests are given in Table III. and was composltlon 30 TABLE III.ABRASIONRESISTANCE OF COATED Example II BEAD MOLDINGS Two-kilograms of beadsfrom Example I were fed to Composition: Wear index 1 (500 cycles) afluidized bed apparatus of the type described in US. A (Control) 208Patent 3,117,027. While the expandable polystyrene beads 35 B 211 weresuspended in a stream of heated air (the tempera- C 136 hire of the airfor each aliquot coated described below), D 163 the air flow at aboutc.f.m. and a nozzle pressure of E 164 about 50-80 p.s.i. Each of thelatices descrlbed below veal. index: were fed to the apparatus through anozzle the lower 40 Wt. loss in mg. 1000 portion of the apparatus. Fourseparate runs, to coat T soles four different aliquots, were made. Aftera specified time, the beads were removed from the apparatus and weighedAll of the coated bead moldings exhibited better abrato determine thepercent by weight of the coating on the slon resistance than thecontrol, except Composition B, beads. All of the coated beads weresuitable for imme- 4 which was comparable to the control. diate feedingto a molding, extrusion or pre-expansion 1. Process for preparingsubstantially uniformly coatdevice for the production of expandedpolystyrene artied expandable polystyrene beads suitable for feedinginto cles. The four coating runs are further described in a mold asdiscrete bead particles comprising: T bl I, (a) suspending saidexpandable polystyrene beads in TABLE I Latex Percent by Air temp. feedrate Time of weight of Composition Lat x F.) (mil/min.) run (min)coating Description of product B Polyethylacrylate T102 pigment 42%solids, 112-118 6 42 5 Smooth, fiat gray, no tack,

0.95 density. adherent film. c Vinyl-chloride vinylidene chlorid opolymr 110 14 30 2.5 Smooth, hin rubbery, (Geon 450 x 23: Goodrich) dilutedto 10.7% no tack, adherent; film. D pfifiith aiene (Poly IBM-10: p er)anionic. 100 8 10 1.5 Waxy, adherent film.

MW 1? 4{111.6%lSQHdlS'tdenstilllyl)loy%li.9l (Dy 110 8 31 2 0 Smoothshiny adherent -t acr ae c E K fi giniz laigl opp ers C0.) 33.5% SO idS-film.

Example III a stream of heated air, said heated air having a tem- Thecompositions of Examples I and II were tested perature of 100-130 F.whereat said beads do not for fusion characteristics and anti-lumpingproperties by appreciably lose their expandable properties; St m moldingdiscs inch thick y 8 Inch f n' (b) contacting said expandablepolystyrene beads with The molding was (lone at secQnds at 20-21 The anaqueous latex so that said beads are coated with results Ofthe moldlngarehstedm Table a layer of said latex and said coated beads are TABLE gf}E ;B ,F QEZ$ XE OF simultaneously dried While in the heated air suspen-L Density sion; and

u m Composition Fusion fitceiit molded p.c.f. (c) removlng said beadsfrom said suspension.

57 L35 2. The process of claim 1 wherein said aqueous poly- 0 i merlatex is a polyethylene latex. 0 1. en 5 2.0 1 3. The process of claim 1wherein said aqueous polyo 1.5

mer latex is a styrene-acrylate copolymer latex.

4. The process of claim 1 wherein said aqueous polymer latex is avinylchloride-vinylidene chloride eopolymer latex.

FOREIGN PATENTS 4/1938 Great Britain. 4/1966 Great Britain.

References Cited UNITED STATES PATENTS 5 WILLIAM D. MARTIN, PrimaryExaminer MATHEW R. P. PERRONE, JR., Assistant Examiner

